Following are some of the key points of the agreement:

SCRAPPAGE INCENTIVES

As a way to take older, polluting cars off the road, carmakers have agreed to offer trade-in deals for older diesel cars if customers then switch to newer, cleaner models.

Ford (>> Ford Motor Company) announced it will pay owners of vehicles with Euro-1, Euro-2 or Euro-3 emission-standard engines a bonus of between 2,000 and 8,000 euros ($2,348 to $9,394) if they trade in their old cars by end of 2017.

BMW said it would pay up to 2,000 euros.

Mercedes-Benz said it would offer customers in Europe up to 2,000 euros for trading in older diesels equipped with engines built to meet the Euro-1 to Euro-4 emissions standards in exchange for a newer Mercedes. A trade-in discount of 1,000 euros will be offered to customers buying an electric Smart car.

Volkswagen said it would offer trade-in discounts of between 2,000 and 10,000 euros for its own-brand cars, depending on the vehicle. For older diesel versions of the VW Golf, a 5,000 euro incentive is being offered.

VW's premium devision Audi said it would offer between 3,000 and 10,000 euros to trade in cars with Euro-4 engines for newer cars, while sister brand Porsche said it would offer up to 5,000 euros.

VW's Seat brand will offer trade-in discounts of between 1,750 euros and 8,000 euros depending on the model.

Opel said it would offer customers between 1,750 and 7,000 euros for trade-ins of cars with Euro-1 to Euro-4 engines, for a newer Opel.

ENGINE SOFTWARE

German carmakers have committed to updating engine management software to make emissions filtering systems operate more effectively. Carmakers had previously made liberal use of a "thermal window" loophole which allowed carmakers to throttle back exhaust emissions management systems in cold weather conditions.

The move will affect 5.3 million cars at a cost of around 500 million euros, with the measures to be funded solely by industry. That includes 2.5 million VW cars that have already been recalled for software updates. The government said the software changes would cut the nitrogen oxide emissions of the affected cars by 30 percent by the end of 2018.

However, environmental group DUH and a Stuttgart regional court have dismissed software updates as being inadequate solutions for tackling pollution. DUH has called the agreement "a grandiose failure", and said it would reduce nitrogen oxide missions by only 2 to 3 percent overall, since it affected less than 20 percent of Germany's 15 million diesel cars. The group said it would continue lawsuits in 16 cities.

Environment minister Barbara Hendricks, from the centre-left SPD, said voluntary software updates can only be a first step, with a more thorough technical update of cars needed to avoid bans in the longer run.

HARDWARE UPGRADES

The government will continue discussions with carmakers on the possible need for more fundamental retrofits - including the addition of extra exhaust-cleaning systems. Such measures are much more expensive than software updates - with the potential costs estimated by analysts as high as 10 billion euros.

TOUGHER TESTING

Germany's KBA vehicle certification authority, which has faced criticism it is not sufficiently independent, will tighten controls of emissions, introducing spot tests of vehicles that have already been approved. The measures were announced when the transport ministry published a report on VW last month.

The agreement does not include a proposal to divide control of certification and emissions testing on the streets, which had been sought by the environment minister.

DIESEL FUND

The auto sector and the government will each contribute half to a 500 million euro fund aimed at helping local governments reduce pollution, including introducing systems to improve traffic flows and improve public transport.

SUBSIDIES

Support for electric buses increased to 100 million euros a year, plus extra backing for hybrid and natural gas buses. Financial incentives to help municipalities and taxi operators fund a switch to electric vehicles are being put in place.

Goal for next legislative period is to create a nationwide network of 50,000 charging points for electric vehicles as well as changes planned to property law to make it easier to install charging points in private buildings.

Support will be provided for trains powered by hydrogen and fuel cells as well as more cash for cycle paths.

(Reporting by Edward Taylor, Gernot Heller and Andrea Shalal; Editing by Keith Weir, David Evans and Georgina Prodhan)